Biodeterioration of Wood - Forest Products Laboratory

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Table 14–2. Types of damage caused by wood-attacking insects Type of damage Description Causal agent Pin holes 0.25 to 6.4 mm (1/100 to 1/4 in.) in diameter, usually circular Tunnels open: Holes 0.5 to 3 mm (1/50 to 1/8 in.) in diameter, usually centered in dark streak or ring in 14–8 surrounding wood Holes variable sizes; surrounding wood rarely dark stained; tunnels lined with wood-colored substance Tunnels usually packed with fine sawdust: Exit holes 0.8 to 1.6 mm (1/32 to 1/16 in.) in diameter; in sapwood of large-pored hardwoods; loose floury sawdust in tunnels Exit holes 1.6 to 3 mm (1/16 to 1/8 in.) in diameter; primarily in sapwood, rarely in heartwood; tunnels loosely packed with fine sawdust and elongate pellets Exit holes 2.5 to 7 mm (3/32 to 9/32 in.) in diameter; primarily sapwood of hardwoods, minor in softwoods; sawdust in tunnels fine to coarse and tightly packed Exit holes 1.6 to 2 mm (1/16 to 1/12 in.) in diameter; in slightly damp or decayed wood; very fine sawdust or pellets tightly packed in tunnels Grub holes 3 to 13 mm (1/8 to 1/2 in.) in diameter, circular or oval Exit holes 3 to 13 mm (1/8 to 1/2 in.) in diameter; circular; mostly in sapwood; tunnels with coarse to fibrous sawdust or it may be absent Exit holes 3 to 13 mm (1/8 to 1/2 in.) in diameter; mostly oval; in sapwood and heartwood; sawdust tightly packed in tunnels Exit holes ~6 mm (~1/4 in.) in diameter; circular; in sapwood of softwoods, primarily pine; tunnels packed with very fine sawdust Exit holes perfectly circular, 4 to 6 mm (1/6 to 1/4 in.) in diameter; primarily in softwoods; tunnels tightly packed with coarse sawdust, often in decay softened wood Nest entry hole and tunnel perfectly circular ~13 mm (~1/2 in.) in diameter; in soft softwoods in structures Ambrosia beetles In living trees and unseasoned logs and lumber Timber worms In living trees and unseasoned logs and lumber Lyctid powder-post beetles Anobiid powder-post beetles Bostrichid powderpost beetles During or after seasoning Damage Begins Ends Usually after wood in use (in buildings) Before seasoning or if wood is rewetted Wood-boring weevils In slightly damp wood in use Roundheaded borers (beetles) Flatheaded borers (beetles) Old house borers (a roundheaded borer) General Technical Report FPL–GTR–190 In living trees and unseasoned logs and lumber In living trees and unseasoned logs and lumber During or after seasoning Woodwasps In dying trees or fresh logs Carpenter bees In structural timbers, siding During seasoning Before seasoning Reinfestation continues until sapwood destroyed Reinfestation continues; progress of damage very slow During seasoning or redrying Reinfestation continues while wood is damp When adults emerge from seasoned wood or when wood is dried When adults emerge from seasoned wood or when wood is dried Reinfestation continues in seasoned wood in use When adults emerge from seasoned wood, usually in use, or when kiln-dried Nesting reoccurs annually in spring at same and nearby locations Network of Systems of interconnected tunnels and chambers Social insects with galleries colonies Walls look polished; spaces completely clean of Carpenter ants Usually in damp partly Colony persists unless debris decayed, or soft- prolonged drying of textured wood in use wood occurs Walls usually speckled with mud spots; some chambers may be filled with “clay” Subterranean termites In wood structures Colony persists Chambers contain pellets; areas may be walled off Dry-wood termites In wood structures Colony persists by dark membrane (occasionally damp wood termites) Pitch pocket Openings between growth rings containing pitch Various insects In living trees In tree Black check Small packets in outer layer of wood Grubs of various insects In living trees In tree Pith fleck Narrow, brownish streaks Fly maggots or adult weevils In living trees In tree Gum spot Small patches or streaks of gum-like substances Grubs of various insects In living trees In tree Ring Double growth rings or incomplete annual layers Larvae of defoliating In living trees In tree distortion of growth insects or flatheaded cambium borers Stained area more than 25.4 mm (1 in.) long introduced by insects in trees or recently felled logs Staining fungi With insect wounds With seasoning
Chapter 14 Biodeterioration of Wood decay. Similarly, pile tops may be protected by treatment with a wood preservative followed by application of a suitable capping compound or shield. Wood boats present certain problems that are not encountered in other uses of wood. The parts especially subject to decay are the stem, knighthead, transom, and frameheads, which can be reached by rainwater from above or condensation from below. Frayed surfaces are more likely to decay than are exposed surfaces, and in salt water service, hull members just below the weather deck are more vulnerable than those below the waterline. Recommendations for avoiding decay include (a) using only heartwood of durable species, free of infection, and preferably below 20% moisture content; (b) providing and maintaining ventilation in the hull and all compartments; (c) keeping water out as much as is practicable, especially fresh water; and (d) where it is necessary to use sapwood or nondurable heartwood, impregnating the wood with an approved preservative and treating the fully cut, shaped, and bored wood before installation by soaking it for a short time in preservative solution. Where such mild soaking treatment is used, the wood most subject to decay should also be flooded with an approved preservative at intervals of 2 or 3 years. During subsequent treatment, the wood should be dry so that joints are relatively loose. Bacteria Most wood that has been wet for a considerable length of time probably will contain bacteria. The sour smell of logs that have been held under water for several months, or of lumber cut from them, manifests bacterial action. Usually, bacteria have little effect on wood properties, except over long periods, but some may make the wood excessively absorptive. This can result in excessive absorption of moisture, adhesive, paint, or preservative during treatment or use. This effect has been a problem in the sapwood of millwork cut from pine logs that have been stored in ponds. There also is evidence that bacteria developing in pine veneer bolts held under water or sprayed with water may cause noticeable changes in the physical character of the veneer, including some strength loss. Additionally, a mixture of different bacteria and fungi was found capable of accelerating decay of treated cooling tower slats and mine timbers. Insect Damage and Control The more common types of damage caused by woodattacking insects are shown in Table 14–2 and Figure 14–8. Methods of controlling and preventing insect attack of wood are described in the following paragraphs. Beetles Bark beetles may damage the surface of the components of logs and other rustic structures from which the bark has not been removed. These beetles are reddish brown to black and Figure 14–8. Types of insect damage most likely to occur in a building. Upper left—Termite attack; feeding galleries (often parallel to the grain) contain excrement and soil. Upper right—Powder-post beetle attack; exit holes usually filled with wood flour and not associated with discolored wood. Lower left—Carpenter ant attack; nesting galleries usually cut across grain and are free of residue. Lower right—Beetle attack; feeding galleries (made in the wood while green) free of residue and surrounding wood darkly stained. vary in length from approximately 1.5 to 6.5 mm (1/16 to 1/4 in.) They bore through the outer bark to the soft inner part, where they make tunnels in which they lay their eggs. In making tunnels, bark beetles push out fine brownish-white sawdust-like particles. If many beetles are present, their extensive tunneling will loosen the bark and permit it to fall off in large patches, making the structure unsightly. To avoid bark beetle damage, logs may be debarked rapidly, sprayed with an approved insecticidal solution, stored in water or under a water spray, or cut during the dormant season (October or November, for instance). If cut during this period, logs should immediately be piled off the ground and arranged for good air movement to promote rapid drying of the inner bark. This should occur before the beetles begin to fly in the spring. Drying the bark will almost always prevent damage by insects that prefer freshly cut wood. Ambrosia beetles, roundheaded and flatheaded borers, and some powder-post beetles that get into freshly cut timber 14–9
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Biodeterioration of Wood - Forest Products Laboratory

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